Aerospace, automobile and medical industries extensively use carbon fabric laminate due to their superior physical and chemical characteristics and, from performance point of view, micro-features are provided on certain components. In this work, an attempt has been made to drill micro-holes in carbon fabric laminate composites using 320 µm diameter carbide drills. Based on a preliminary study, drilling strategy with peck cycle is chosen for through-hole drilling in carbon fabric laminate. Micro-drilling experiments are conducted according to full-factorial design using five levels for both speed and feed with three trials for each condition. Thrust force and torque generated during machining are measured and power law based regression models are developed. Though the material is anisotropic and non-homogeneous in nature, the models developed follow the trend in the experimental results. Delamination damage, roundness error and diameter of these drilled holes are measured and analyzed with variation of the process parameters. The results indicate that the good quality micro-holes can be produced by selecting proper process parameters.
Aerospace and automobile industries extensively use components made of plastics and fiber-reinforced plastics which require micro-machining operations including microdrilling to be carried out. Various attempts are reported in the literature to study different strategies and model the forces in micro-drilling with a view to produce micro-holes having large aspect ratio and to reduce drill breakage. The force models are more statistical than mechanistic in approach. In the present work, an attempt is made to develop mechanistic models of thrust and torque in micro-drilling of plain epoxy sheets. Material model capturing strain rate and temperaturedependent yield strength of epoxy material and basic principles of machining are employed for this purpose. The mechanistic model for prediction of thrust and torque is validated using well-planned full factorial design of experiments. Experiments are carried out using a carbide drill of 0.5-mm diameter with three levels for speed and feed on a highspeed miniature machine tool specially developed at the laboratory. The material model is extended to glass-reinforced plastics (GRP), and drilling forces are predicted using the proposed mechanistic model. In both cases of plain and GRP sheets, the model predictions are close to the experimentally measured drilling forces.
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